Study On Separation Of Ethylene Glycol And 1,2-Butanediol Mixture

Ethylene glycol and 1,2-butanediol are two important organic chemical raw materials.In the process of producing ethylene glycol from coal resources,by-products such as 1,2-butanediol will be formed.When ethylene glycol is produced from biomass,a mixture of ethylene glycol,propylene glycol and series butanediol is obtained after preliminary separation of the product.These by-products have high boiling points which are very close to each other,so it is difficult to separate them by conventional separation methods.Among them,the separation of ethylene glycol-1,2-butanediol system is the most common and thorny problem in the process of polyols production.In order to obtain ethylene glycol with high purity,a feasible separation technique needs to be developed,and the vapor-liquid equilibrium data of the mixture of ethylene glycol and1,2-butanediol is the basis for developing the separation process.In this paper,FL9790 gas chromatograph with FID detection methods was employed as the main analytical equipment to quantitatively analysis research system,the instrument analytical parameters were adjusted previously,and the calibration relationship between these component content and test information was confirmed for the research systems,respectively.Vapor-liquid equilibrium data of ethylene glycol-1,2-butanediol mixture system at 100.4 kPa and 30.4 kPa,and that of ethylene glycol-n-octanol mixture system at 30.4 kPa were measured consecutively by KM-VL-1equilibrium still.In order to rapidly fit the phase equilibrium data obtained,the model fitting function of Aspen Plus software was studied,and the separation process of glycol-1,2-butanediol mixture was established and optimized based on the phase equilibrium experiment data of the research system.Thermodynamic consistency of three groups of data was tested by integral test method.The results were less than 10% and passed thermodynamic Consistency Test.The NRTL model in Aspen Plus software was selected to fit the measured vapor-liquid equilibrium data and obtain the model parameters.The vapor-liquid equilibrium data of ethylene glycol-1,2-butanediol system at 100.3 kPa were calculated by the obtained model(The average deviation and maximum relative deviation of experimental and calculated values of liquid phase ethylene glycol are 0.0041% and 0.0135%,respectively),vapor-liquid equilibrium data of ethylene glycol-1,2-butanediol system at30.4 kPa(The average deviation and maximum relative deviation of experimental and calculated values of liquid phase ethylene glycol are 0.0162% and 0.0650%,respectively),vapor-liquid equilibrium data of ethylene glycol-n-octanol at 30.4 kPa(deviation and maximum relative deviation of experimental and calculated values of liquid phase ethylene glycol are 0.0093% and 0.0239%,respectively),and the fitting result was ideal.Firstly,the variable-pressure distillation simulation and optimization of the mixture of ethylene glycol and 1,2-butanediol were carried out by using Aspen Plus software,and the process flow of the alternating separation between components in the atmospheric column and the reduced pressure column was determined.The optimum parameters of atmospheric tower process simulation are: operating pressure is 100.4 kPa,theoretical plate number is 50,feed position is in the range of 28-34,reflux ratio is 6.5;the optimum parameters of vacuum tower process simulation are: operating pressure is30.4 kPa,theoretical plate number is 55,feed position is between 20-34,reflux ratio is3.Under these conditions,the mass purity of ethylene glycol can reach 99 wt% after the mixture is separated by atmospheric distillation column,and the mass purity of1,2-butanediol can reach 98 wt% after further separation by vacuum distillation column,to meet industrial requirements.The azeotropic distillation process of ethylene glycol-1,2-butanediol mixture was simulated and optimized by Aspen Plus software.N-octanol was used as azeotropic agent in separation,and azeotropic distillation process was established.The optimized process parameters are as follows: operating pressure is 30.4 kPa,theoretical tray number is 17,feed position is the eighth theoretical tray,reflux ratio is 0.9.Under the condition of the process parameters,the mass fraction of 1,2-butanediol in the top of the column is less than 2wt% and the content of ethylene glycol in the reactor product is less than 0.1wt%.The results of this study provide two solutions for the separation technology of ethylene glycol-1,2-butanediol mixture system.